U.S. Pat. No. 2,331,597, issued Oct. 12, 1943, to G. Coles, for "Disintegrator Hammer" describes a rotary hammer mill with hammers pivotally connected with a rotor. Another hammer mill with hammers pivoted to a rotor about an axis at a radial distance from the axis of the central shaft of the rotor is shown in U.S. Pat. No. 4,973,005, issued Nov. 27, 1990, to F. Haesebrouck et al., for "Hammer-Crusher Rotor."